Effect Of Close-to-nature Transformation Of Larch Monoculture Stands On Regeneration And Plant Diversity

The change of the forest floor plant diversity and regeneration in Larix gmelinii monoculture plantations was surveyed in Dailing, after conduction of close-to-nature stand transformation with different gap sizes (100 m2,50 m2,25 m2) and various soil disturbances, with conventional uniform thinning as control. In addition, we investigated the effect of two different sizes thinning gaps (138.1±11.2 m2 and 51.0±10.8 m2) on regeneration and plant diversity in the uniform thinning of 34-yr-old Larix olgensis monoculture plantations, respect to uniform thinning controls, eight years after thinning. The objective of above researches was to explore close-to-nature transformation methods of Larch Monoculture Stands in Northeat China.1 The results of Close-to-nature Transformation of Larix gmelinii Monoculture Stands are as follows:(1) A substantial increases in species number, quantity, cover, mean height and diversity index of herbaceous plants were detected in the close-to-nature transformed stands in the 2nd year after thinning(P<0.05), however no significant differences in that of woody plants were detected between close-to-nature and uniform transformations(P>0.05).(2) Among the dominant herbaceous plants, important value of hygrophilous ones increased dramatically in the gap transformed stands; Little change was found in the dominant woody plants.(3) No significant differences were detected with species number, quantity, cover, mean height and diversity index of herbaceous plants under different gap treatments(P>0.05). In the 1st year after transformation, significant greater increases were found in quantity,cover and mean height of herbaceous plants under the floor scratching treatment in comparison to that with no scratching(P<0.05); but the differences diminished in the 2nd year.(4) No significant differences were detected in favor regeneration between close-to-nature and uniform transformations, or among different close-to-nature transformations (P>0.05).2 The results of combination of uniform thinning and gap thinning of Larix oglensis Monoculture Stands are as follows:(1) The thinning gap made good effects in favor regeneration, especially large gap. The individual density, mean height and mean basilar of seedlings in large gaps increased substantially by 28.4%,78.2% and 69.7%(P<0.05), respectively, which had no differences except individual density increased by 20.4% in small gaps(P>0.05).(2) In general, the thinning gap significantly improved the understory plant diversity(P<0.05). The Simpson's diversity index, the coverage of understory woody plants and the coverage of herbaceous plants were significantly greater in thinning gaps than in controls(P<0.05), except for the coverage of herbaceous plants in small gaps. Compared with small gap, substantial increases in the coverage of woody plants (increased by 42.8%) and herbaceous plants (31.3%) were detected in large gap(P<0.05). (3) Changes in functional groups of forest floor plants among large gaps, small gaps and controls were observed. For important value of Competitor species in under woody plant layer, the size ranking is, large gap>small gap>control, the opposite for Stress-resistant species, significantly different(P<0.05). In herbaceous plants layer, important values of annuals plants species and ruderals species were significantly higher in large gaps than in small gaps and controls(P<0.05), however perennials plants species and stress-resistant species were significantly lower(P<0.05). There were no clear differences in composition of Life forms and Grime's strategy between small gaps and controls(P>0.05).In summary, our results suggest that gap thinning transformation favor the regenerantion and promotes the diversity, and combination of uniform thinning and gap thinning is more suitable for transformation of the larch plantation with high density.